1. Field of the Invention
The present invention relates to a rubber gasket for a fuel cell for sealing configuring members of the fuel cell.
2. Description of the Related Art
In a fuel cell, a cell in which an electrode member including a membrane electrode assembly (MEA) is sandwiched between separators serves as a unit for power generation. The fuel cell is configured by stacking a number of cells. A frame-shaped rubber gasket is arranged at the periphery of the electrode member and between the adjacent separators to ensure sealability and insulating property with respect to gas and cooling medium. For example, Japanese Patent Application Publication Nos. 2005-50728 (JP 2005-50728 A) and 2012-195128 (JP 2012-195128 A) and Japanese Patent Publication No. 4530122 (JP 4530122 B) describe a rubber gasket including a seat portion and a lip portion.
FIG. 13 shows a cross-sectional view of the rubber gasket in a height direction described in JP 2005-50728 A as an example of a conventional rubber gasket. As shown in FIG. 13, a rubber gasket 9 is arranged on a surface of a separator 94. The rubber gasket 9 includes a seat portion 90 and a lip portion 93. The lip portion 93 is a two-stage rounded portion including a first hill portion 91 and a second hill portion 92. A curvature radius R2 of the second hill portion 92 is smaller than a curvature radius R1 of the first hill portion 91. Assuming a perpendicular line drawn from a center C2 of curvature of the second hill portion 92 to the separator 94 is a central axis A of the second hill portion 92, a center C1 of curvature of the first hill portion 91 also lies on the same central axis A. In other words, the center C1 of curvature of the first hill portion 91 and the center C2 of curvature of the second hill portion 92 are on the same central axis A. The seat portion 90 includes a horizontal surface 900 leading in a horizontal direction from a bottom of the first hill portion 91.
When a fuel cell is in an assembled state, the rubber gasket is compressed in the height direction by the adjacent separator. In this case, the rubber gasket is required to have a wide range of usable compression rates. In other words, at the time of high compression in which a pressing force from the separator is large and the compression rate of the rubber gasket is high, it is demanded that the lip portion that makes elastic contact with the separator does not break easily. At the time of low compression in which the pressing force from the separator is small and the compression rate of the rubber gasket is low, on the other hand, it is demanded that the lip portion is compressed in the height direction without being bent and without collapsing, and that the sealability is ensured by the reaction force of the rubber gasket.
However, in the conventional rubber gasket having the shape shown in FIG. 13, strain tends to concentrate at the interior of a connecting portion between the first hill portion and the seat portion, thus causing the lip portion to easily break at the time of high compression. At the time of low compression, on the other hand, the lip portion is not compressed in the height direction (central axis A direction in FIG. 13) so it tends to fold and collapse, and the sealability is difficult to ensure. Thus, the range of compression rates at which the rubber gasket can be used is limited.